Despite minor setbacks in use of copper integrated circuits, the semiconductor industry, together with associated research institutions, are progressively solving current problems and are adopting copper as a next generation semiconductor material. With this trend as a driving force, there is a need to develop advanced solutions to address current and future health, economic, and environmental issues that are associated with copper and other metal-bearing waste.
In the semiconductor manufacturing industry, treatment of wastewater containing heavy metal ions and abrasive solids to meet discharge levels (as mandated by EPA and local authorities) has been continuously challenging, sometimes unreliable and often expensive. This is mainly due to time wasted and operating costs associated with the chemical conditioning of wastewater during processing, such as use of mineral acids for wastewater pH adjustment and use of expensive polishing agents. Other costs arise from membrane treatment to reduce fouling, metals recovery from ion exchange and general costs resulting from high capital equipment maintenance, such as filter bed replacement.
In attempts to solve economic and environmental problems associated with treating chemical mechanical planarization (CMP) wastewater, several methods and chemical compositions for removing metals ions from waste streams are currently in use.
For instance, Grinstead, in U.S. Pat. No. 4,741,831 teaches a cyclic process for treating an aqueous metal-bearing waste stream which comprises: 1) contacting the aqueous waste stream with a polymeric chelant to form a soluble metal complex, 2) using membrane separation to remove the aqueous portion, 3) contacting the concentrate with a mineral acid to release the metal, 4) using a second membrane filtration to separate the metal filtrate from the regenerated polymeric chelant, and 5) recycling the aqueous polymeric chelant concentrate to the contact zone of the first step.
Allen et al. in U.S. Pat. Nos. 5,871,648; 5,965,027; 6,312,601 and 6,428,705 teach processes for removing metal and non-metal contaminants from wastewater comprising: 1) adjusting pH of the wastewater stream and treating it with an organic or inorganic coagulant to form a particulate (or agglomerate) in excess of 5 microns in size, 2) passing the treated wastewater through a microfiltration membrane to remove the contaminants, and 3) periodically back-flushing the microfiltration membrane to remove the solid contaminants from the membrane surface. This technology operates in a single pass, with no reconcentration mode. The preferred organic polymeric coagulants, by way of example, are poly[epichlorohyrin-co-dimethylamine] (pEPI/DMA) and poly[diallyldimethylamonium chloride] (pDADMAC) polymers. It is further taught that, for metal containing waste, it may be desirable to add a metal removal agent to yield an insoluble metal precipitate that is absorbed by the coagulant. In the examples with CMP slurries, the chemical treatments are added directly to the slurry and then processed directly via microfiltration.
Salmen et al., in U.S. Pat. No 6,258,277 teach a process for removing heavy metals from a semiconductor wastewater containing abrasive solids comprising: 1) adding an effective amount of a water-soluble polymer containing dithiocarbamate functionality (DTC-polymer), 2) precipitating heavy metal ions, and 3) passing wastewater through a microfilter to remove the abrasive solids and precipitated heavy metal ions. It is further taught that the use of a coagulant in conjunction a DTC-polymer will adversely affect permeate flux and quality.
Carey et al., in U.S. Pat. No. 5,594,096 teaches a composition effective for removing metals from wastewater comprising the dithiocarbamate analogs of poly[ethylenimine]. It is further noted in the teachings that filtering the treated wastewater can enhance the efficiency of the metals removal.
Smith et al., in PCT WO 96/38493 discloses a number of water-soluble polymers, including poly[ethylenimine] derivatized with chelating functionality for use in separating metals from aqueous streams. It is further disclosed that the permeate flux of a treated waste stream through an ultrafiltration membrane can be enhanced by “prepurifying” the polymer before derivatization to remove low molecular weight species. Example 2 (polymer B) of WO '493 is compositionally equivalent to the polyethyleiminodiacetic acid.XNa (PEIDA) composition of the present invention.
Quamme et al., U.S. Pat. No. 4,558,080; Kelly et al., U.S. Pat. Nos. 4,734,216 and 4,781,839; and Chen et al. in U.S. Pat. No. 5,916,991 teach derivatized tannin containing polymer compositions that are effective coagulants for clarification of wastewater.
The use of cationic polymers and anionic polymers as coprecipitants in removing heavy metals from wastewater is known in the art. For instance, Swanson et al. (U.S. Pat. No. 3,947,354) use a cationic polyelectrolyte and anionic xanthate to precipitate and remove metal ions from wastewater. However, Swanson et al.'s selection of anionic polymers is limited to water soluble polyhydroxyl derivatives, such as starch, cellulose, dextrins, hemicellulose, polyvinyl alcohols and preferably anionic starch xanthate.
A drawback to current technologies for treating CMP wastewater is that the copper is coprecipitated with abrasive solids, thus increasing the amount of copper-containing waste generated. Furthermore, current technologies require utilization, with periodic maintenance, of the ion exchange bed to successfully remove copper to compliance level. Thus, it is an object of the present invention to provide a process for treating CMP wastewater that minimizes the amount of copper-containing waste generated. A further object of the present invention is to provide a novel treatment for CMP wastewater.